Headlight dimming devices



Nov. 17, 1959 R. D. MORROW HEADLIGHT DIMMING DEVICES Filed Feb. 29, 1956 mmllllm myzmon Robert D. Morrow HEADLIGHT DIMMING DEVICES Robert D. Morrow, Pittsburgh, Pa., assignor to Morrow Products, Inc., Pittsburgh, Pa.

Application February 29, 1956, Serial No. 568,508

4 Claims. (Cl. 317-124) The present invention relates to headlight dimming devices and particularly to devices for dimming the headlights of motor vehicles automatically in response to light emanating from another source such as, for example, an oncoming vehicle. The problem of controlling the lighting level of automotive vehicle headlights has long troubled the automotive industry. Various attempts have been made to provide a headlight dimming device which would automatically lower the level of light produced by automobile headlights upon the approach of another vehicle. These dimming devices have, however, not been entirely satisfactory. The dimming devices which have been proposed have used photomultiplier circuits and have been expensive, relatively large in size, and not sutficiently sensitive to color and light. In addition, difiiculties have arisen due to sensitivity to temperature changes within the devices as well as externally of the devices, so that the devices have not been completely stable.

The present invention provides a dimming device which overcomes all of the problems outlined above. It is sufficiently sensitive to dim the headlights at the desired light level. There is no warm up delay and no temperature sensitivity, and the response of the device is sufiiciently rapid and stable under automotive operating conditions and will outlive the life of an ordinary automobile.

I provide a three stage transistor amplifier having a first stage push-pull connection, and two succeeding stages operated at a gain factor less the maximum. A photocell is provided to receive light from the emanating source to convert the light energy to electrical energy which is fed to the input of the push-pull amplification stage. Preferably, the photocell is in series with a transistorized oscillator whose output is rectified and filtered.

I have pointed out certain features, advantages and objects of my invention in the foregoing statement. Other advantages, objects and purposes will be apparent from a consideration of the following description and the accompanying single figure of the drawing which is a line drawing of a circuit for the dimmer device of my invention. Referring to the drawing, I have illustrated a cadmium sulphide photocell 10 adapted to receive light from an emanating source.

The photocell 10 is in series with a 90 volt DC. power supply generally indicated at A. The power supply is a transistorized inductance capacitance oscillator deriving its power from a 12 volt D.C. battery 11. The output of the oscillator is transformed to 90 volts, rectified and filtered through rectifiers 12 and 13 and filter condensers 14 and 15.

The output from the photocell 10 is carried to a first stage of amplification B consisting of two transistors 21 and 22 in push-pull connection. This push-pull connection compensates for drift due to temperature changes of the transistor which characteristics are very pronounced at low input levels. The transistors 21 and 22 are selected to have similar characteristics and to operate at the same temperature. A variable resistor 23 is placed across the output side of transistor 21. A similar renited States Patent sistor 24 is connected across the output side of resistor 22. This makes it possible to compensate for slight differences in the transistors 21 and 22 so that their characteristics can be exactly matched. Resistors 25, 26, 27 and 28 are placed in the input side of the tube transistors so as to etfect current bias to accentuate the efiect of the input current in the transistors 21 and 22. The output voltage from transistors 21 and 22 developed across resistors 23 and 24 is fed into a second amplification stage C into a transistor 29. The output current from stage C is fed into a third stage of amplification D through a current limiting resistance 30. The output of the transistor 29 goes to a transistor 31 in the third stage of amplification; from the transistor 31, the output is fed through a limiting resistor 32 to a control relay 33. The limiting resistors 30 and '32 are introduced for the purpose of limiting the current output through transistors 29 and 31, thereby protecting transistor 31 from overload. These limiting resistors are set to saturate the last stage of amplification at about 8 ma.

The dimmer device specifically described above has sufficient gain to energize the relay 33 at a distance of about 1500 feet from an oncoming automobile headlight or at about feet from a rear tail light. If the car battery voltage is dropped to 11 volts, the relay will still be energized at 1000 feet. If, on the other hand, the voltage is raised to 17 volts, the relay will not be energized beyond about 2000 feet.

While I have illustrated and described a present preferred embodiment of my invention, it will be understood that it may be otherwise embodied within the scope of the following claims.

I claim:

1. An automatic vehicle headlight dimming system operative from a vehicle battery supply comprising in combination, means converting the supply voltage to a higher voltage level, a phototube receiving current from the converting means and positioned to receive light from a light emanating source, a pair of transistors in pushpull connection forming an amplification stage receiving the output from the phototube, a third transistor amplifier receiving the output from said push-pull amplification stage, a fourth transistor amplifier receiving the output from the third transistor amplifier and a dimmer relay coil receiving the output from the fourth transistor amplifier to operate a dimmer switch.

2. An automatic vehicle headlight dimming system operative from a vehicle battery supply comprising in combination a transistorized inductance capacitance oscillator adapted to raise the supply voltage to a higher voltage level, a rectifier and filter means receiving the voltage from the oscillator, a phototube receiving current from the rectifier and filtering means and positioned to receive light from a light emanating source, a pair of transistors in push-pull connection connected to the phototube and receiving current therefrom for amplification, a third transistor amplifier connected to the push-pull amplification stage and receiving the output therefrom, a fourth transistor amplifier receiving the output from the third transistor amplifier and a dimmer relay coil receiving the output from the fourth transistor amplifier whereby to actuate a dimmer switch.

3. An automatic vehicle headlight dimming system operative from a vehicle battery supply comprising in combination, means converting the supply voltage to a higher voltage level, a phototube receiving current from the converting means and positioned to receive light from a light emanating source, a first amplification stage including two transistors in push-pull connection, a resistance across the output side of each transistor, at least one of which resistances is a variable resistance whereby output changes due to temperature variations may be ed to regulate the current passing to the transistor in the third amplification stage and a dimmer relay coil receiving the output from the third amplification stage to operate a dimmer switch.

' 4. An automatic vehicle headlight dimming system operative from a vehicle battery supply comprising in combination, means converting the supply voltage to a higher voltage level, a phototube receiving current from the converting means and positioned to receive lightfrom a light emanating source, a first amplification stage including two transistors in push-pull connection, a resistance across the output side of each transistor, at least one of which resistances is a'variable resistance whereby output changes due to temperature variations may be compensated, a second amplification stage connected to the output from the first amplification stage and receiving the output therefrom, the second amplification stage including a transistor amplifier, a third amplification stage connected to the output ofthe transistor of the second amplification stage, said third amplification stage including a transistor amplifier, said second and third amplification stages having current limiting resistance means acting on two stages whereby to limit the current gain to a value below the breakdown value of the transistors therein, and a dimmer relay coil receiving the output from the third amplification stage to operate a dimmer switch.

References Cited in the file of this patent UNITEDSTATES PATENTS OTHER REFERENCES Transistorized Headlight Dimmer, Radio and Television News, pp. 56, 57 and 122, August 1955. 

